IRRIG8: Sprayline Evaluation

With the whole set operating: at the first test point or sprinkler downstream of the hydrant, at a sprinkler in the middle, and at the last sprinkler. Include the highest and lowest parts of the field. Use a pitot gauge at a sprinkler. If regulators are fitted, read the sprayline pressure upstream of the regulators (sprayline pressure cannot be inferred from readings at a regulated sprinkler); sprinkler pressure is then taken as the lower of that reading and the regulator setting.

Flow q = Kd × p^x. Used to turn the sprayline pressures into flows (pressure distribution uniformity). Determine Kd and x from the test below, or enter the manufacturer’s values. Without either, x = 0.5 is used (the Code’s value for most sprinklers); Kd is then only needed for flows in litres.

At least four adjacent sprinklers of the same specification near the middle of one sprayline, avoiding the inlet end. Shroud each with a loose hose and collect for at least 30 seconds or 20 litres. Repeat with the sprayline pressure changed by about 20%, then reset the system.

Measured flows from sprinklers spread along the length of a sprayline. Four or more give a measured flow distribution uniformity (QDUlq), which is used in the field DU instead of the pressure-derived value.

A collector identical to the test collectors, with a known volume of water, placed upwind of the test area. Each wet collector is corrected by the evaporation rate × the time from when the system was shut off to when it was read.

A grid of collectors between three correctly working adjacent sprinklers on a representative part of the sprayline. Rows run across the sprayline; the first row is half a row spacing from the first test sprinkler and the last half a row spacing from the third (e.g. 5 rows over 2 sprinkler spacings).

In each row the first collector is half a collector spacing off the sprayline and the last is half a spacing outside the wetted radius, on both sides. Shut the system off before reading collectors.